The present invention relates generally to flame detectors and specifically to an apparatus for conducting radiation from the combustion zone of a burner to a detector device.
An essential element in the safety and control of boilers used in power generating equipment, and the like, is the ability to reliably detect the existence of flame at the burner. A detector of this sort, which has proved remarkably effective, is disclosed in a co-pending application of Horn, U.S. Ser. No. 425,039, filed Dec. 14, 1973. This detector is, as well as others may be, utilized in conjunction with the present invention in those applications where a straight line of sight may not be available to view a selected burner combustion zone.
In the above noted application, the combustion zone was selected for its useful concentration of infrared radiation. While it is not intended to limit the present invention to that portion of the spectrum, it is a useful area to discuss for purposes of explanation.
In certain boilers, burners are constructed so as to be movable during firing and it has been found that a useful area of the combustion zone may not be within the line of sight of the detector at all times. The invention disclosed herein therefore is especially useful for these applications.
The choice of a fiber optic system seems a reasonable beginning for such a system. However, various difficulties revealed themselves in the course of development. One especially troublesome problem was the transmission characteristics of the energy transmitted. For example, energy outside the visible spectrum is required for an accurate determination of the existence of a main burner flame in many applications, however, many fiber optic materials were found to attenuate the energy so drastically as to render the signals obtained essentially useless. Conventional fiber optics materials proved unsatisfactory. Other materials exhibiting proper transmission characteristics were not suited for adaptation to a fiber optics application.
Another major difficulty encountered was the high temperature environment within the boiler which would fuse the bundle and render it ineffective.
In addition to the foregoing difficulties, there are limits to which different bundles of optics may be flexed and for a particular size of the individual fibers, these considerations added to the constraints in the development of the subject of the present invention.
The present invention was developed so as to be adaptable with the highly effective detector described above in the Horm application. However, other detectors responsive to radiant energy may be used. For example, in the present invention, since the attenuation of the energy transmittal is extremely low from one end of the fiber optics bundle to the other, it can be said that any detector system which can directly view the flame or burner combustion zone can also be utilized with the present invention in the event that it is necessary to place the detector remotely from the combustion zone of the burner.
In addition to the foregoing, it has been found that fiber optics have a tendency to exhibit substantial optical losses unless each of the fibers in the optics bundle is clad with a material which reduces interference between adjacent fibers in the bundle. The cladding, however, has a tendency to deteriorate in the hostile environment of a furnace burner area. With certain fiber optics materials, therefore, it has been found that unsatisfactory optical communication is exhibited, thus rendering some systems ineffective to transmit a sufficient quantity of radiation from the combustion zone to a remote receiving device.
It is therefore an object of the present invention to provide a flame detection system for use with burners of a movable type.
It is another object of the present invention to provide a flame detection system wherein the detector may be remotely located from the burner combustion zone.
It is another object of the present invention to provide a flame detector apparatus wherein energy from a selected area of the combustion zone is communicated to the detector for reliable indication of the existence of a flame.
It is yet another object of the present invention to provide a flame detector apparatus utilizing an improved optical system capable of transmitting sufficient quantities of radiation for detection of a flame.